1. Field of the Invention
The present invention relates to a reluctance type rotating machine equipped with permanent magnets, which is compact with a high output and which is capable of rotating in a wide range by its adoption of a new pole structure.
2. Description of the Related Art
As shown in FIG. 1, an earlier reluctance type rotating machine comprises a stator 1 having armature windings 2 and a salient-pole rotor 3 having an uneven core 4 since the rotating machine does not require coils for forming a field system about the rotor 3. Therefore, the reluctance type rotating machine is simple in structure and low in price.
We now describe a principle of producing the output of the reluctance type rotating machine. Because of unevenness about the rotor, the reluctance type rotating machine exhibits small magnetic reluctance at protrusions of the rotor and large magnetic reluctance at recesses of the rotor. That is, there is a difference of stored magnetic energy between a gap over the protrusion and another gap over the recess. The output of the reluctance type rotating machine comes from the change in magnetic energy. Note, the protrusions and recesses may be provided by a configuration allowing the unevenness to be formed not only geometrically but magnetically, in other words, the configuration where the magnetic reluctance and distribution of magnetic flux density vary depending on the position of the rotor.
As another high-performance rotating machine, there is a permanent magnet type rotating machine. In the rotating machine, a plurality of permanent magnets are arranged on the substantial whole periphery of the rotor core although the armature windings of the machine is similar to the armature windings of an induction machine, the same windings of the reluctance type rotating machine, etc.
Due to the unevenness about the core surface, the reluctance type rotating machine has different magnetic reluctance which depends on the rotational position of the rotor. This change in magnetic reluctance causes the magnetic energy to be varied thereby to produce an output of the rotor.
In the conventional reluctance type rotating machine, however, the increasing of currents causes a local magnetic saturation to be enlarged at the protrusions of the rotor 4. Thus, the enlarged magnetic saturation also causes magnetic flux leaking to the recesses between poles to be increased, so that effective fluxes are decreased while lowering the output power.
On the other hand, as another high-powered rotating machine, there is a permanent magnet type rotating machine using xe2x80x9crare-earth metal xe2x80x9d permanent magnets having high magnetic energy products. Owing to the arrangement of the permanent magnets on the surface of the rotor core, when the permanent magnets of high energy are employed to form a magnetic field, the permanent magnet type rotating machine is capable of forming an intense magnetic field in an air-gap of the machine, providing a compact and high-powered rotating machine.
Nevertheless, it should be noted that a voltage induced in the armature windings gets larger in proportional to the rotating speed of the rotor since the magnetic flux of each magnet is constant. Therefore, if the machine is required to operate at a wide range of variable speeds up to the high-speed rotation, it is difficult to carry out the xe2x80x9crated-output xe2x80x9d operation of the machine at a rotating speed twice or more as large as the base speed under constant current and voltage.
It is therefore an object of the present invention to provide a reluctance type rotating machine which is compact in spite of high output and which is capable of operating at a wide range of variable speeds.
To achieve the object of the present invention described above, from the 1st aspect of the invention, there is provided a reluctance type rotating machine comprising:
a stator having armature windings;
a rotor having a rotor core, the rotor being provided, in a circumferential direction thereof, with a magnetic unevenness;
a plurality of permanent magnets arranged in the rotor core, for negating the armature windings"" flux passing between adjoining poles defined in the rotor, each of the permanent magnets being magnetized in a direction different from a direction to facilitate the rotor""s magnetization; and
wherein a magnetic portion is ensured in the rotor core so that, when the armature windings are not excited, more than 30% (percent) of the permanent magnets"" flux is distributed in the rotor and also that, when the machine is loaded, the permanent magnets"" interlinkage flux is more than 10% of composite interlinkage flux composed of current and the permanent magnets.
It is noted that the above composite interlinkage flux is changed by a phase difference between the flux vector of current and the flux vector of permanent magnets. Therefore, we now define the amount of composite interlinkage flux when both phases exerting no influence on each other are on the crossing condition at a right angles, as the above composite interlinkage flux of the invention.
As the magnetic unevenness is formed about the rotor core, a magnetic protrusion of the unevenness constitutes a pole of a reluctance motor, while a magnetic recess does an interpole (i.e. a part between the adjoining poles) of the motor. Namely, the magnetic protrusion corresponds to a xe2x80x9ceasy-magnetizingxe2x80x9d direction to facilitate the rotor""s magnetization, while the magnetic recess corresponds to a xe2x80x9chard-magnetizingxe2x80x9d direction where it is difficult to magnetize the rotor.
According to the invention, the permanent magnets are arranged in the magnetic recesses in the rotor core. Additionally, in the rotor core, there is provided a magnetic portion for closing the permanent magnets"" flux in a short circuit so that, when the armature windings are not excited, more than 30% (percent) of the permanent magnets"" flux is distributed in the rotor. With this structure, it is possible to reduce an induced voltage generating at the rotor""s rotating to 0 to 70% of the rated voltage for the rotating machine. For example, under condition that the induced voltage is set to 33%, even if rotating the rotating machine at high speed of three times as fast as the base speed, there would be no possibility to apply an excessive current to an electric circuit.
Next, when the machine is loaded, the above magnetic portion is intensely subjected to the magnetic saturation by the flux due to the load current. Consequently, the permanent magnets"" flux distributing between the poles does increase. According to the invention, the magnetic portion between the poles constitutes a magnetic path so that a part of permanent magnets"" flux is distributed in the direction of the center-axis of interpole. Additionally, the magnetic portion is adapted in a manner that, when the machine is loaded, the permanent magnets"" interlinkage flux is more than 10% of composite interlinkage flux composed of armature current and the permanent magnets.
The flux of each permanent magnet has an action to repulse the armature current flux entering along the center-axis direction of the interpole and increase the magnetic reluctance in the direction of the magnet since the relative permeability of the magnet is generally equal to zero. Thus, since the permanent magnets"" flux and the armature flux in the opposite direction cancel each other, the composite flux along the center-axis direction of the interpole gets fewer or flows in a direction opposite to the armature current when the armature current is small.
Therefore, since the interlinkage flux along the center-axis direction of the interpole gets smaller, a change within the magnetic unevenness about the rotor is so enhanced that the output of the machine does increase. On the other hand, the armature flux has a tendency of distribution to pass through the magnetic protrusions of the rotor core in concentration. Consequently, as the unevenness of flux density about the air-gap is promoted, the magnetic-energy change becomes larger to provide the machine with high torque and high power factor.
As to an adjusting range of terminal voltage required for operating the machine at a wide range of variable speeds, the function will be described below.
According to the invention, since the permanent magnets are embedded in the interpoles locally, the surface area of the permanent magnet on the peripheral side of the rotor is smaller than that of the conventional rotating machine where the permanent magnets are arranged about the whole periphery of the rotor surface, so that the interlinkage flux by the magnets gets fewer, too. Then, the interlinkage flux due to the armature current (both exciting current component and torque current component of the rotating machine) takes part in the interlinkage flux of the permanent magnets, so that a terminal voltage is induced.
In the permanent magnet type rotating machine, it is possible to adjust the terminal voltage because the interlinkage flux of the permanent magnets occupies almost the whole terminal voltage. On the contrary, since the rotating machine of the invention has a small interlinkage flux of the permanent magnets, it is expected that when adjusting the exciting current widely, then it is possible to control terminal voltage in a wide range. That is, since the exciting current component can be adjusted so that the voltage is less than a power source voltage corresponding to the velocity, the rotating machine is capable of operating at a wide range of variable-speeds under the power source of constant voltage. Additionally, since a part of each permanent magnet flux leaks through the above-mentioned magnetic portion forming the short circuit, it is possible to reduce diamagnetic field inside the permanent magnet. Thus, since an operating point on a demagnetizing curve expressing the B(magnetic flux)xe2x88x92H(field intensity) characteristics of the permanent magnet is elevated (causing a large permeance coefficient), the demagnetizing-proof characteristics with respect to both temperature and armature reaction is improved. Particularly, in case of canceling the permanent magnets"" flux by the armature current forming the flux in the directions of the interpole-axes, it is possible to prevent the demagnetization of the rotor although the demagnetizing field is applied on the magnets.
Furthermore, since the permanent magnets are embedded in the rotor core, it acts as a retaining mechanism of the permanent magnets, so that the rotating machine can ensure its high-speed operation.
According to the 2nd aspect of the invention, there is provided a reluctance type rotating machine comprising:
a stator having armature windings;
a rotor having a rotor core, the rotor being provided, in a circumferential direction thereof, with a magnetic unevenness;
a plurality of permanent magnets arranged in the rotor core, for negating armature flux passing between adjoining poles defined in the rotor, each of the permanent magnets being magnetized in a direction different from a direction to facilitate the rotor""s magnetization; and
wherein a magnetic portion is ensured in the rotor core so that, when the armature windings are not excited, more than 80% (percent) of the permanent magnets"" flux is distributed in the rotor and also that, when the machine is loaded, the permanent magnets"" interlinkage flux is more than 5% of composite interlinkage flux composed of current and the permanent magnets.
Although the basic function of this rotating machine is similar to that the previously-mentioned rotating machine, the induced voltage is remarkably small because more than 80% of the permanent magnets"" flux is distributed in the rotor when the armature windings are not excited. Consequently, even if the short circuit is caused in the power source or so, a current originating in the voltage induced by the permanent magnets is so insignificant to prevent the machine from being burned or braked excessively. Further, since the stator core loss caused by the magnets"" flux gets fewer, the machine""s efficiency can be improved when it is under unloaded or slight-loaded condition.
In addition, the magnetic portion is adapted in a manner that, when the machine is loaded, the permanent magnets"" interlinkage flux is more than 5% of composite interlinkage flux composed of armature current and the permanent magnets. Since the magnets"" flux and the armature flux cancel each other under the loaded condition, the composite flux in the directions of center axes of the interpoles is reduced.
Consequently, because of reduced interlinkage flux in the direction of center axes, the magnetic unevenness about the rotor is enhanced to increase the output of the machine. Simultaneously, since the interlinkage flux in the direction of center axes of the interpoles is decreased, the terminal voltage is lowered, whereby the power factor of the machine can be improved. Again, the current flux is distributed so as to pass through the poles in concentration.
From the above, as the change in flux density of the gap is increased in the present invention, the change in magnetic energy is also increased thereby producing high torque and high power factor.
Furthermore, this rotating machine can perform the following action. Since almost all the flux of each permanent magnet leaks through the magnetic portion of the short circuit, it is possible to reduce diamagnetic field inside the permanent magnet remarkably. Thus, since an operating point on the demagnetizing curve expressing the B(magnetic flux)xe2x88x92H(field intensity) characteristics of the permanent magnet is also elevated (causing a large permeance coefficient), it is possible to use the permanent magnets having a deteriorated temperature characteristic, at a temperature of 50 to 200xc2x0 C. Even if flowing a large current of two or three times as large as a rated current in an atmosphere of high-temperature, there is no possibility that the permanent magnets are demagnetized owing to the armature reaction. Especially under a condition of the rated torque current, if increasing the armature current in order to accomplish a maximum torque of several times as much as the normal torque in case of negating the permanent magnets"" flux by the armature current forming the flux in the directions of interpoles, there is produced a gap flux in the opposite direction to the interlinkage flux of the permanent magnets by the armature current. In such a case, the rotating machine of the embodiment allows the permanent magnets to be used without being demagnetized.
Also in this rotating machine, since the permanent magnets are embedded in the rotor core, it acts as the retaining mechanism of the permanent magnets, so that the rotating machine can ensure its high-speed operation.
According to the 3rd aspect of the invention, there is provided a reluctance type rotating machine comprising:
a stator having armature windings;
a rotor having a rotor core, the rotor being provided, in a circumferential direction thereof, with a magnetic unevenness;
a plurality of permanent magnets arranged in the rotor core, for negating the armature windings"" flux passing between adjoining poles defined in the rotor, each of the permanent magnets being magnetized in a direction different from a direction to facilitate the rotor""s magnetization; and
wherein, in a magnetic flux of the permanent magnets at an air gap, an amplitude in a fundamental component of a magnetic flux density of the permanent magnets is 0.2 to 0.6 T.
According to the 4th aspect of the invention, in common with the above-mentioned rotating machines, the magnetizing direction of the permanent magnets is substantially identical to the circumferential direction of the rotor. In this case, since the flux of exciting current component passing the poles intersects the magnetizing direction of the permanent magnets in substantial right angles in electrical angle, the magnetic saturation due to the current is eased at the respective poles, so that the reluctance torque grows larger.
According to the 5th aspect of the invention, the rotor is provided, between the adjoining poles, with a first non-magnetic part. Owing to the provision of the first non-magnetic part at each interpole, the magnetic reluctance in the direction of the interpoles is remarkably increased. Therefore, since a large unevenness is produced in flux density at the gap, it is possible to produce a large output of the machine because of the increased change in magnetic energy.
According to the 6th aspect of the invention, a width of each pole is 0.3 to 0.5 times as long as a pole pitch which corresponds to a circumferential distance from a center of an pole to a center of the adjoining pole.
With this establishment of the pole and interpole, it is possible to effectively increase the change in the gap flux density with respect to the position of the rotor, where the rotating machine of high output can be provided.
According to the 7th aspect of the invention, the rotor has magnetic portions each formed on the periphery between the adjoining poles, for magnetically connecting therebetween. Owing to the provision of the magnetic portions, the magnetic material uniformly spreads over the whole periphery of the rotor with respect to core teeth of the stator. Consequently, the change of magnetic reluctance caused by slots of the stator gets smaller while decreasing the slot ripple. Further, the smooth surface of the rotor allows the windage loss to be reduced. It is also possible to restrict the demagnetizing field, which is caused by the armature current acting on the permanent magnets, owing to the magnetic portions outside the interpoles.
According to the 8th aspect of the invention, the rotor is provided with a second non-magnetic part for reducing flux leaking through respective inward portions of the permanent magnets in the radial direction. Owing to the provision of the non-magnetic part on the inner end of each permanent magnet, it is possible to prevent the flux from leaking out of the magnet. Therefore, it is possible to reduce a volume of the permanent magnet without remarkably deteriorating the characteristic of the machine.
According to the 9th aspect of the invention, the first non-magnetic part between the adjoining poles is positioned so as not to increase magnetic reluctance outside the permanent magnets remarkably.
Since the first non-magnetic part does not increase the magnetic reluctance outside the magnet, it is possible to ensure sufficient flux in spite of small quantity of permanent magnets.
Further, by the first non-magnetic part, the permanent magnets"" flux is distributed in the rotor""s surface opposing the stator when the armature windings are not excited. When the flux due to the load current overlaps, each magnetic portion between the pole and the interpole and the outer magnetic portion are subjected to the magnetic saturation, so that the permanent magnets"" flux closing in the rotor interlinks with the stator. Therefore, when the machine is not loaded, the induced voltage due to the interlinkage flux of the permanent magnets is so small, whereby the flux of the permanent magnets can be utilized effectively under the loaded condition.
According to the 10th aspect of the invention, a gap length outside the interpole of the rotor is larger than the gap length outside the pole.
Since the gap length outside the pole is smaller than the gap length outside the interpole, the magnetic unevenness is further enlarged, so that the reluctance torque does increase. When the armature windings are not excited, the permanent magnets"" flux interlinking with the armature windings is decreased thereby to close in the rotor core through the magnetic portion between the adjoining poles because the gap length outside the interpole is relatively long.
When the flux of current overlaps at the time of the machine being loaded, the rotor is locally subjected to the magnetic saturation, so that the permanent magnets"" flux closing in the rotor is brought into the interlinkage with the stator. Therefore, when the machine is not loaded, the induced voltage due to the interlinkage flux of the permanent magnets is so small, whereby the permanent magnets"" flux can be effectively increased under the machine""s loaded condition.
According to the 11th aspect of the invention, the reluctance type rotating machine is characterized in that the flux due to an armature current in a center axis-direction between the adjoining poles and the flux of the permanent magnets negates each other, so that the composite flux in the center axis-direction is substantially equal to zero.
When applying the load current, the flux of the armature current negates the permanent magnets"" flux, so that the composite flux in the center axis of the interpole amounts to zero. Therefore, the voltage induced by the flux in the central axis of the interpole becomes to be zero, too. Thus, since the terminal voltage is induced by the flux in the direction of pole, low voltage and high output can be provided for the rotating machine.
Additionally, the constant output characteristic can be obtained with ease. As the reluctance torque is a product of both exciting current and torque current component of the armature, the output is obtained by a product of the exciting current, the torque current component and the rotating speed Upon fixing the armature current component (torque current) forming the flux in the direction of interpole axis into a constant value so that the composite flux in the direction of center axis of the interpose amounts to zero, by adjusting the armature current component (exciting current) with respect to the rotating speed in inverse proportion to each other, the constant output characteristic where torque times rotating speed is constant can be accomplished.
According to the 12th aspect of the invention, under condition that an armature current component forming the flux in the central axis-direction between the adjoining poles becomes a maximum, the flux due to the armature current component in the center axis-direction between the adjoining poles and the flux of the permanent magnets negates each other, so that the composite flux in the center axis-direction is substantially equal to zero.
In this case, the maximum current for the rotating machine is divided into two vector components crossing at right angles, i.e., an armature current component forming the flux in the direction of center axis of the interpole and another armature current forming the flux in the direction of pole. When the maximum current of armature (composite vector) intersects the armature current component forming the flux in the direction of center axis of interpole at angles of 45 degrees, a maximum of reluctance torque can be obtained. The rotating machine of the invention is constructed in a manner that, at this current phase, the flux of armature current in the direction of the central axis of the interpole negates the flux of each permanent magnet and therefore, the resultant composite flux in the interpole direction amounts to substantial zero. Therefore, when the induced voltage is raised during the machine""s operation at a high rotating speed range, the machine allows the armature current component (i.e. exciting current component) forming the flux in the direction of pole to be adjusted smaller, whereby the constant induced voltage can be attained. Consequently, it is possible to operate the machine at a wide range of variable-speeds and realize the high power factor while maintaining the constant output.
According to the 13th aspect of the invention, in connection with the armature current produced by the flux of the permanent magnets when the machine is electrically closed in a short circuit, the interlinkage of magnetic flux produced by the permanent magnets in case of the armature current of zero interlinking with the flux of the permanent magnets is determined in a manner that heat derived from Joule-loss originating in the armature current is less than a thermal allowable value of the machine or braking force produced by the armature current is less than an allowable value in the rotating machine.
If the permanent magnets"" flux which interlinks with the armature windings exists when an electrical short-circuit accident is caused in an inverter, a terminal or the like, the rotation of the rotor causes an induced voltage to be generated. Due to this induced voltage, the short-circuit current may flow in the armature windings for burning or an operation of the apparatus may be locked by excessive brake torque. According to the invention of the 1st and 2nd aspects, since the high output of the machine is accomplished by the interlinkage flux from small number of permanent magnets, it is possible to reduce the induced voltage in order to establish both short-circuit current and brake less than the allowable values, respectively. Consequently, even if occurring the short-circuit accident, it would be possible to prevent troubles in the rotating machine and the apparatus.
According to the 14th aspect of the invention, the permanent magnets are arranged between the adjoining poles and the first non-magnetic part between the poles is provided with a conductive material.
With the arrangement of the conductive material in the first non-magnetic magnetic part, an eddy current is generated in the conductive materials when the rotor does not synchronize with the rotating field, so that the rotor can enter its synchronous rotation. That is, the self-starting and stable rotation of the rotating machine can be realized.
According to the 15th aspect of the invention, the rotor is provided, on a periphery thereof, with a plurality of conductive members extending in the axial direction of the rotor.
Since the induced current flows in the conductive members at the machine""s asynchronous operation, the self-starting and stable rotation of the rotating machine can be realized. Further, it is possible to absorb the eddy current by harmonic current when driving the inverter.
According to the 16th aspect of the invention, the reluctance type rotating machine further comprises a pair of magnetic end rings arranged on respective axial ends of the rotor.
When the rotor is subjected to an armature reaction field in the opposite direction to the magnetized direction of each permanent magnet in the rotor core by the armature current, a part of magnetic flux of the permanent magnets forms closed magnetic paths each flowing the core in the axial direction, entering into the end ring and returning the core. That is, since the leakage flux can be produced effectively, it is possible to adjust the amount of interlinkage flux between the armature windings and the permanent magnets, whereby the terminal voltage can be controlled by the armature current with ease. In addition, it is possible to adjust the ratio of leakage flux to effective flux by controlling a clearance between the rotor core and each end ring.
According to the 17th aspect of the invention, the object of the present invention can be also accomplished by a reluctance type rotating machine comprising:
a stator having armature windings;
a rotor having a rotor core, the rotor being provided, in a circumferential direction thereof, with a magnetic unevenness;
a plurality of permanent magnets arranged in the rotor core along directions of respective poles of the rotor, for negating armature flux passing between adjoining poles defined in the rotor; and
wherein each interpole between the adjoining poles has an outer face recessed with respect to an outer face of the pole in the radial direction of the rotor.
According to the above invention, since the outer face of each xe2x80x9cinterpolexe2x80x9d (or an inter-pole portion) of the rotor is recessed with respect to the outer face of the xe2x80x9cpolexe2x80x9d (or a magnetic pole portion) in the radial direction of the rotor, a gap length in the radial direction of the rotor between the stator and the rotor changes, so that the magnetic unevenness is formed about the rotor. While, since the permanent magnets are magnetized so as to negate the armature flux passing the xe2x80x9cinterpolesxe2x80x9d (i.e. interpole portions), each magnetic reluctance in the direction along each interpole is increased. Thus, an unevenness is produced in the magnetic flux density at the gap between the stator and the rotor, whereby a great torque can be produced in the rotating machine by the resultant change in magnetic energy.
According to the 18th aspect of the invention, in the rotating machine of the 17th aspect, each of the permanent magnets is arranged so as to leave a part of the rotor core between an outer end of the permanent magnet in the radial direction of the rotor and an outer periphery of the rotor.
According to the 19th aspect of the invention, in the rotating machine of the 18th aspect, the part between the outer end of the permanent magnet and the outer periphery of the rotor has a radial thickness to be magnetically saturated by the armature flux.
According to the 20th aspect of the invention, in the rotating machine of the 18th aspect, it is preferable that the part between the outer end of the permanent magnet and the outer periphery of the rotor has a radial thickness smaller than a radial thickness of the interpole at a center thereof.
According to the 21st aspect of the invention, in the rotating machine of the 18th aspect, it is preferable that the part between the outer end of the permanent magnet and the outer periphery of the rotor has a radial thickness so that, when no current flows in the armature windings, the magnetic flux density of the permanent magnets interlinking with the armature windings gets less than 0.1 T at the gap between the rotor and the stator.
In common with the 18th to 21st aspects of the invention preferable arrangements, owing to the provision of a part of core between each permanent magnet and the outer periphery of the rotor, the flux from the magnet is closed in the rotor core when the armature current is zero, in other words, the machine is unloaded. Thus, since the induced voltage in the armature windings is substantially equal to zero, the rotating machine allows the rotor to rotate at a constant speed without being braked from the stator""s side. Further, even if an electrical short-circuit occurs the armature windings, an inverter, etc. during the rotor""s rotation, the short-circuit current does not flow since the induced voltage is substantially equal to zero. Therefore, in spite of the short-circuit, it is possible to prevent an excessive braking force from being produced and the armature windings from being damaged. When the machine is loaded, the armature flux in the directions of the poles partially passes through the outer core portion outside the permanent magnets, so that each interpole is magnetically saturated at both ends of the interpole in the circumferential direction. Consequently, the flux of the permanent magnets is distributed out of the rotor and interlinks with the armature windings, whereby the output and power factor of the machine can be improved.
According to the 22nd aspect of the invention, in the machine of any one of the 18th to 21st aspects, each of the permanent magnets is arranged so as to form a space between the outer end of the permanent magnet and the outer periphery of the rotor, in addition to the part of the rotor core.
According to the 23rd aspect of the invention, the space is filled up with a non-magnetic material.
According to the 24th aspect of the invention, a cavity is formed in each interpole portion of the rotor core.
In the above cases, since the cavity or the non-magnetic material acts as the magnetic reluctance, it is possible to reduce the leakage flux flowing from the pole to the interpole effectively.
According to the 25th aspect of the invention, the object of the present invention described above can be also accomplished by a reluctance type rotating machine comprising:
a stator having armature windings;
a rotor having a rotor core, the rotor being provided, in a circumferential direction thereof, with a magnetic unevenness and also defining magnetic poles and interpoles in the rotor core by turns;
a plurality of permanent magnets arranged in the rotor core along directions of respective poles of the rotor, for negating armature flux passing between adjoining poles defined in the rotor; and
a conductor arranged on a peripheral portion of the rotor core, for generating an induced current in the conductor.
With the above-mentioned arrangement of the conductor, an induced electromotive force is produced in the conductor owing to the electromagnetic induction at the machine""s starting, thereby accomplishing the self-starting of the rotating machine.
While, since the permanent magnets are magnetized so as to negate the armature flux passing the interpoles, each magnetic reluctance in the direction along each interpole is increased to produce an unevenness in the magnetic flux density at the gap between the stator and the rotor. Thus, a great torque can be produced in the rotating machine by the resultant change in magnetic energy.
According to the 26th aspect of the invention, in the machine of the 25th aspect, the conductor is constituted by a plurality of magnetic bars which are embedded in the vicinity of an outer face of each pole of the rotor core so as to extend in the axial direction of the rotor.
In this case, owing to the provision of the magnetic bars as the conductor, the machine is capable of self-starting by their conductivity. Additionally, as the bars are made of magnetic material, the density of flux (main flux) flowing the poles is not reduced, so that there is no possibility to exert an influence on the machine torque.
According to the 27th aspect of the invention, in the machine of the 26th aspect, the rotor has cavities formed in respective core portions outside the permanent magnets in the radial direction of the rotor.
In this case, the magnetic circuit is interrupted by each of the cavities, so that the magnetic reluctance of the interpoles is further increased. Therefore, the change in magnetic energy between each pole and each interpole is so increased thereby to generate a great torque.
According to the 28th aspect of the invention, in the machine of the 27th aspect, the rotor core is provided, in the vicinity of an outer face of each interpole, with a plurality of non-magnetic conductor bars extending in the axial direction of the rotor and generating an induced current therein.
In this case, owing to the addition of the non-magnetic conductor bars, the self-starting characteristic of the machine is further progressed. Further, the non-magnetism of the bars allows the magnetic reluctance of the interpoles to be increased furthermore, so that the change in magnetic energy is further increased.
According to the 29th aspect of the invention, in the machine of the 28th, aspect, the cavities of the rotor are filled up with part a plurality of non-magnetic conductor bars extending in the axial direction of the rotor and generating an induced current therein.
In this case, since the magnetic circuit is interrupted by the non-magnetic conductor bar in each cavity, the magnetic reluctance of the interpoles is further increased in comparison with the case of only providing the cavities in the interpoles. Further, the strength of the rotor per se is improved by embedding the bars in the cavities.
According to the 30th aspect of the invention, in the machine of the 25th aspect, the conductor comprises a plurality of deep groove magnetic bars which are embedded in the vicinity of an outer face of each pole of the rotor core so as to extend in the axial direction of the rotor and a plurality of non-magnetic bars which are embedded in the vicinity of an outer face of each interpole of the rotor core so as to extend in the axial direction of the rotor.
In this case, since the conductive bars are embedded along the whole periphery of the rotor core, the starting capability similar to a case of using an exclusive starting cage can be attained by the conductivity of the bars. Further, owing to respective material choices for the poles and interpoles, a difference in magnetic reluctance between each pole and each interpole is increased. Consequently, the change in magnetic energy is further increased.
According to the 31st aspect of the invention, in the machine of the 25th aspect, the conductor is constituted by a plurality of non-magnetic bars which are embedded in the vicinity of an outer face of each interpole of the rotor core so as to extend in the axial direction of the rotor.
In this case, the magnetic reluctance in the interpoles is increased by the non-magnetism of the non-magnetic bars. Further, since the poles is provided with no bar, the structure of the rotor is simplified.
According to the 32nd aspect of the invention, in the machine of the 25th aspect, the conductor is adapted so as to cover an outer face of the rotor core.
In this case, since the induced current flows in the outer periphery of the rotor smoothly due to the conductivity of the conductor at the machine""s starting, the machine is capable of starting by itself. In addition, since the rotor is covered with the conductor, the mechanical strength of the rotor can be improved.
According to the 33rd aspect of the invention, in the machine of the 32nd aspect, the conductor has a cylindrical shape so as to cover the whole outer face of the rotor core.
Then, in addition to the improved self-starting capability, the cylindrical conductor allows the mechanical strength to be improved with its simple structure.
According to the 34th aspect of the invention, in the machine of the 32nd aspect, the conductor is constituted by a plurality of shell members connected with the outer faces of the poles to cover the interpoles.
In this case, since the shell members are connected with the outer faces of the poles, the air resistance (or windage loss) during the rotor""s rotation is reduced thereby to enhance a rotational efficiency of the rotor.
According to the 35th aspect of the invention, in the machine of the 25th aspect, the conductor is arranged in the vicinity of an outer face of each interpole of the rotor core and curved along the circumferential direction of the rotor.
In this case, when the machine is starting, the induced current flows in the interpoles, allowing the self-starting of the rotor.
According to the 36th aspect of the invention, in the machine of the 25th aspect, the conductor has a plurality of slits formed in a cylindrical portion of the rotor core and arranged along the circumferential direction of the rotor.
Due to the formation of the slits, the induced current at the machine""s starting flows while defining a long path in the axial and circumferential directions of the rotor. Consequently, the magnetic coupling between the armature windings and the rotor is reinforced to provide a great starting torque for the rotor.
According to the 37th aspect of the invention, in the machine of the 36th aspect, the conductor is formed so as to cover the outer face of the rotor core.
In this case, since the induced current flows in the outer periphery of the rotor smoothly, it facilitates the self-starting of the machine furthermore. In addition, since the rotor is covered with the conductor, the mechanical strength of the rotor can be further improved.
According to the 38th aspect of the invention, in the machine of the 37th aspect, the conductor has a cylindrical shape so as to cover the whole outer face of the rotor core.
Then, in addition to the improved self-starting capability, the cylindrical conductor allows the mechanical strength to be improved with its simple structure. Moreover, the air resistance (or windage loss) during the rotor""s rotation is reduced thereby to enhance the rotational efficiency of the rotor.
According to the 39th aspect of the invention, in the machine of the 38th aspect, the conductor is constituted by a plurality of shell members connected with the outer faces of the poles to cover the interpoles.
Also in this case, since the shell members are connected with the outer faces of the poles, it is possible to reduce the air resistance (or windage loss) during the rotor""s rotation, whereby the rotational efficiency of the rotor can be enhanced.
According to the 40th aspect of the invention, in the machine of the 36th aspect, the conductor is arranged in the vicinity of an outer face of each interpole of the rotor core and curved along the circumferential direction of the rotor.
Also in this case, when the machine is starting, the induced current flows in the interpoles, allowing the self-starting of the rotor.
According to the 41th aspect of the invention, in the machine of the 37th or the 38th aspect, the conductor is made of conductive magnetic material.
Then, it is possible to make the rotor""s magnetic reluctance against the main flux smaller while making the main flux larger. Furthermore, since the slipping gets smaller at the machine""s pulling-in, the machine is capable of starting and pulling-in with respect to such a load as requiring a large torque to drive.
According to the 42nd aspect of the invention, the object of the present invention described above can be also accomplished by a reluctance type rotating machine comprising:
a stator having armature windings;
a rotor consisting of a rotor core and an annular member outside the rotor core; and wherein
the rotor core includes a plurality of poles each consisting of a core portion projecting outward in the radial direction of the rotor and a plurality of interpoles each disposed between the adjoining poles in the circumferential direction of the rotor; and
the annular member is fitted to the rotor core so as to surround the peripheries of the poles.
In this case, since the peripheries of the poles of the rotor core is covered with the annular member, the interpoles of the rotor is reinforced to allow the bridge portions of the interpoles to be thinned. Therefore, the leakage of the q-axis flux through the bridge portions is reduced to enhance the magnetic reluctance of the interpoles.
According to the 43rd aspect of the invention, in the machine of the 42nd aspect, the rotor is provided, on respective side faces of the poles in the circumferential direction, with a plurality of permanent magnets which are magnetized so as to negate armature flux passing through the interpoles.
In this case, since the permanent magnets"" flux opposes the q-axis flux, the magnetic reluctance in the interpoles is enhanced to improve the output of the machine.
According to the 44th aspect of the invention, in the machine of the 40th. aspect, the annular member is made of magnetic material.
In this case, the d-axis flux is easy to pass through the pole portions, so that the main flux can be increased.
According to the 45th aspect of the invention, in the machine of the 42nd. aspect, the annular member is constituted by material of which saturation flux density is lower than that of material forming the rotor core.
In this case, the resultant rotor (rotor core and annular member) has a lowered saturation flux density in the bridge portions in comparison with the conventional rotor where the adjoining poles are connected with each other through the rotor core material in the interpole. Thus, the magnetic reluctance can be enhanced in spite of the bridge portions of the identical thickness.
According to the 46th aspect of the invention, there is also provided a method of manufacturing a rotor of a rotating machine, comprising the steps of:
preparing a rotor core having a plurality of poles each consisting of a core portion projecting outward in the radial direction of the rotor and a plurality of interpoles each disposed between the adjoining poles in the circumferential direction of the rotor;
arranging a plurality of permanent magnets before magnetization on respective side faces of the poles in the circumferential direction of the rotor,
setting the rotor core on a magnetizing unit thereby to magnetize the permanent magnets; and thereafter,
fitting an annular member to the rotor core in a manner that the annular member surrounds the peripheries of the poles.
Since the rotor core to be prepared in the above method is provided with the pole projecting outward in the radial direction of the rotor and the interpoles each disposed between the adjoining poles, it is possible to approach the pre-magnetized magnets, which are attached to the rotor core, to a magnetizer easily, facilitating the magnetizing operation for the permanent magnets.
According to the 47th aspect of the invention, there is also provided a method of manufacturing a rotor of a rotating machine, comprising the steps of:
preparing a rotor core having a plurality of poles each consisting of a core portion projecting outward in the radial direction of the rotor and a plurality of interpoles each disposed between the adjoining poles in the circumferential direction of the rotor;
arranging a plurality of permanent magnets after magnetization on respective side faces of the poles in the circumferential direction of the rotor; and thereafter,
fitting an annular member to the rotor core in a manner that the annular member surrounds the peripheries of the poles.
Also in this case, it is possible to easily insert the magnetized magnets into spaces each interposed between the poles from the outside in the radial direction of the rotor, facilitating the assembling operation of the rotor.
These and other objects and features of the present invention will become more fully apparent from the following description and appended claims taken in conjunction with the accompany drawing.